664823921 has 4 divisors (see below), whose sum is σ = 673931172. Its totient is φ = 655716672.

The previous prime is 664823917. The next prime is 664823953. The reversal of 664823921 is 129328466.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 513656896 + 151167025 = 22664^2 + 12295^2 .

It is a cyclic number.

It is not a de Polignac number, because 664823921 - 2² = 664823917 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (664823911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4553516 + ... + 4553661.

It is an arithmetic number, because the mean of its divisors is an integer number (168482793).

Almost surely, 2^664823921 is an apocalyptic number.

It is an amenable number.

664823921 is a deficient number, since it is larger than the sum of its proper divisors (9107251).

664823921 is an equidigital number, since it uses as much as digits as its factorization.

664823921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9107250.

The product of its digits is 124416, while the sum is 41.

The square root of 664823921 is about 25784.1796650582. The cubic root of 664823921 is about 872.7748286806.

The spelling of 664823921 in words is "six hundred sixty-four million, eight hundred twenty-three thousand, nine hundred twenty-one".